Nowadays, increasing attention is paid to synthetic polymers for the development of artificial organs and the formulation of medicaments [Chem. Eng. News 2001, 79 (6), 30]. The polymers concerned must satisfy a certain number of criteria and, in particular, they must be biocompatible. Biodegradable character is an additional advantage if the polymer must be eliminated after an appropriate period of implantation in an organism. In this respect, copolymers based on lactic and glycolic acid (PLGA) are of great interest as they are susceptible to hydrolysis and are degraded in vivo with the release of non-toxic by-products. The field of application of PLGAs is very wide (Adv. Mater. 1996, 8, 305 and Chemosphere 2001, 43, 49). In the surgical field, they are used for the synthesis of multi-strand wires, sutures, implants, prostheses etc. In pharmacology, they allow the encapsulation, transfer and controlled release of active ingredients.
For all these applications, the key factor is the degradation rate of the PLGAs which of course depends on their structure (chain length, dispersity, proportion, stereochemistry and chain formation of the monomers etc.). In the last few years, numerous works have therefore been devoted to the development of catalysts and/or primers of (co)polymerization, i.e. lactide and/or glycolide polymerization or copolymerization, making it possible to prepare PLGAs with a controlled structure.
The use of metallic systems most often leads to a contamination of the copolymers thus obtained by the presence of metal salts, which sometimes constitutes a significant limitation depending on the applications envisaged. The development of non-metallic systems allowing the controlled (co)polymerization of lactide and/or glycolide therefore constitutes a major challenge. The present invention comes within this context.
The Applicant therefore proposes the use of a simple catalytic system, constituted by a (co)polymerization catalyst and additive, and which makes it possible to control the chain length but also the nature of the chain ends of the prepared (co)polymers.